Vitol spokesman Donald Goldberg told United Press International via email that the company was working with South Sudan's government on the project.
"Vitol is working with the government of Sudan to review the next phases of implementation of a small refinery project in South Sudan," said Goldberg. "Vitol has completed the basic design of the project."
The company didn't offer specifics on the project's refining capacity.
South Sudan, independent since July 2011, halted oil production in January in response to alleged stealing by the Sudanese government. South Sudan controls most of the regional oil fields though Sudan has the export infrastructure.
Both sides this month approved a cooperation agreement signed in September that paves the way for the resumption of exports of oil from South Sudan through Sudanese transit networks.
Border issues, ethnic conflicts and disputes over oil threatened to derail the 2005 peace agreement that secured South Sudan's independence.